1. Field of the Invention
The present invention relates in one aspect to methods and an apparatus for writing and verifying servo frames written on a storage medium. In another aspect, the present invention relates to methods and apparatus for verifying data areas of a storage medium. In yet another aspect, the present invention relates to methods and apparatus for writing and verifying servo frames and data areas of a storage medium.
2. Description of the Related Art
Information for systems such as data processing systems is typically stored on storage media. Particular use is made of storage disks such as magnetic disks, opto-magnetic disks, and the like. One type of magnetic disk arrangement is a so-called “head disk assembly” which is intended normally to be permanently fixed in a data processing system; the head disk assembly includes one or more magnetic disks and the associated “product” head or heads having read and write elements which read data from and write data to the disk. Another type of magnetic disk arrangement is of a type known as “removable media” which normally consists of a magnetic disk medium in a protective plastics case and which can be used to transfer data between data processing systems by physical transfer of the disk itself from one machine to another.
In a known method of manufacturing storage media such as hard disk drives, a head disk assembly consisting of the product head(s), the disk or disks, the motor and arm electronics, is mounted in a mastering station known as a servo-writer. The servo-writer causes the write element of the product head to write plural servo frames around each track on the disk. The servo frames provide the master reference that is used by the disk drive during normal operation in order to locate the tracks and sectors on the disk for data storage and retrieval. Clearly, the servo frames have to be accurately written to the disk at very well defined positions. Currently, it takes over 35 minutes to write the complete set of servo frames to a typical disk.
It is of course desirable to be able to verify at least some if not all of the servo frames. However, at present, this can only be done after the servo track writing process is completed, for the reasons discussed below.
The product write element has to have a width that is less than the pitch (i.e. the width) of the tracks of the disk so that the product write element when in use by an end user only writes data to a single track and does not overwrite data on adjacent tracks. Typically, the width of the write element is about 70% to 80% of the track pitch. This means that during the conventional servo track writing process described above, the servo frames have to be written in two passes for each track. More specifically and starting at say the outside diameter of the disk, a first (outer) half of the servo frames are written on a first pass over the track, the product write element is moved inwards half a track, and the second (inner) half of the servo frames are written in a second pass over the track. Accordingly, given that the product write element is effectively writing the whole time that it is passing over locations of the servo frames on the tracks of the disk, the servo frames can only be verified after all of the servo frames have been written to the disk. In practice, such verification is not carried out, or is only carried out to a limited degree by verifying a sample of the servo frames, because of the time that would be taken following the conventional servo track writing process.
For both cost and performance benefits, there is a trend towards use of a so-called media level servo track writer to write the servo tracks to storage media, such as disks. The media level writer writes the servo frames prior to the disk being incorporated in a hard disk drive. The media level writer thus has its own head having at least a write element for writing the servo tracks to the disk in place of the product write element that is used in the conventional servo track writing process described above. A media level writer typically has a gang of heads for writing to plural disks simultaneously but could be a single head disk combination.
It is desirable to carry out a so-called media certification of the disk, i.e. to check the data areas of the disk for defects, such as surface defects, substrate defects, mechanical scratches, etc. At present, this is carried out on a separate media certification machine prior to the servo writing process and, in a typical example, takes an additional 15 minutes or so to check the whole of the data areas. Bearing in mind that the disk has to be physically moved from the media certifier to the servo track or media level writer, a complete media certification process would add some 50% to the processing time required to prepare the disk. This is obviously undesirable. Time savings can be made by checking only a sample of the data areas, but ideally the whole of the data area is checked.